SPRING Working Group J. Dong
Internet-Draft Z. Du
Intended status: Standards Track Huawei Technologies
Expires: January 23, 2020 July 22, 2019
SRv6 for Inter-Layer Network Programming
draft-dong-spring-srv6-inter-layer-programming-00
Abstract
This document defines a new SRv6 network function which can be used
for SRv6 inter-layer network programming. It is a variant of the
End.X function. Instead of pointing to an L3 adjacency, this
function points to an underlay interface. Such a interface can stand
for a underlay link or path/connection between two routers, which may
be invisible in the L3 topology.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language and Terminology . . . . . . . . . . . . 3
3. END.XU Function . . . . . . . . . . . . . . . . . . . . . . . 3
4. Use Case for SRv6 Underlay Interface Function . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
In many scenarios, operator owns a multi-layered network. In that
case, cross-layer design and optimization mechanisms are more
efficient in resource utilization and SLA assurance, but normally are
also considered more complicated. As an IP/MPLS based technology,
Segment Routing (SR) normally does not need to care about the network
layers beneath the IP layer. One exception is as described in
[I-D.ietf-isis-l2bundles], IS-IS is extended to advertise the link
attributes and Segment Identifiers (SIDs) of Layer 2 (L2) bundle
members, so that operator can control traffic flows to traverse a
particular individual L2 link which comprises the L2 bundle interface
In [I-D.ietf-spring-srv6-network-programming], it is described that
for an outgoing interface bundle made of 10 member links, up to 11
End.X local SIDs for that bundle need to be allocated. One END.X for
the bundle itself and then up to one END.X for each member link.
However, there are some differences between the normal END.X function
for the bundle and the END.X function for the member link, as they
are not at the same network layer. Moreover, besides the L2 bundle
use case, there are other types of underlay interfaces or
connections, which can be integrated and programmed using SRv6. This
document aims to define a unified SRv6 function to support those
inter-layer network programming in SRv6.
As another example, the underlay of the IP network can be an optical
network. In many today's IP and optical transport networks, IP
network and optical network are maintained separately, and in most
cases, the optical network works as an underlay which is invisible to
the IP network. However, the optical path resource and the IP path
resource may not be one-to-one mapped so that some resource in
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optical network can not be fully used. In some cases, there may be
some optical paths that is not visible in the L3 IP topology, and
thus they can not be used to carry IP traffic.
Following the SRv6 network programming concept in
[I-D.ietf-spring-srv6-network-programming], we can use a new SRv6
function to identify a specific optical path, and put the
corresponding SRv6 SID into an integrated SRv6 SID list. The optical
path can be either OTN based or DWDM based. Besides the optical
paths, it is also possible to use the SRv6 function to identify other
underlay paths/connenctions, such as a back-to-back Ethernet
connection, or some pre-configured tunnels.
The SRv6 function mentioned above can be considered as a variant of
the END.X function defined in
[I-D.ietf-spring-srv6-network-programming], so that it is suggested
to define a new SRv6 function for it. This document defines the
operation of this new SRv6 function, and describes some use cases of
this SRv6 underlay interface function.
2. Requirements Language and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119] when they appear in ALL CAPS. When these words are not in
ALL CAPS (such as "should" or "Should"), they have their usual
English meanings, and are not to be interpreted as [RFC2119] key
words.
3. END.XU Function
This section defines the new SRv6 underlay interface function.
The "Endpoint with cross-connect to an underlay interface" function
(End.XU for short) is a variant of the End.X function defined in
[I-D.ietf-spring-srv6-network-programming].
When N receives a packet destined to S and S is a local End.XU SID, N
does:
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1. IF NH=SRH and SL > 0
2. decrement SL
3. update the IPv6 DA with SRH[SL]
4. forward to underlay interface bound to the SID S
5. ELSE IF NH!=SRH
6. Send an ICMP parameter problem message; drop the packet
7. ELSE
8. drop the packet
Note that the underlay interface or connection in step 4 SHOULD be
established before this function is announced into the network.
This End.XU function can be announced using IGP or BGP-LS in a
similar way to the announcement of END.X function. The detailed
protocol extension will be described in a separate document.
4. Use Case for SRv6 Underlay Interface Function
Assuming that an operator owns both the IP and optical network, and
the operator needs to deploy E2E service across IP and optical
network, with traditional approaches the planning and service
provisioning would be complex and time consuming due of the manual
synergy needed between the operator's IP team and optical team. With
the popularity of SR and SRv6, one straightforward way is to use a
SID list that integrates the path in both the IP layer and the
optical layer.
As the optical layer is not packet based, normally source routing
mechanism can not be directly used in the optical network. However,
we can expose the abstracted optical path and its associated
attribute and resource information into the network control system of
the IP network, by using the SRv6 End.XU function defined in this
document, so that E2E inter-layer paths can be programmed to meet
some specific traffic's SLA, such as low latency.
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----- ----- -----
| P1 |--------| P2 |--------| P3 |
----- ----- -----
/ |. |. |. \
----- / | . | . | . \ -----
| P7 | | . | . | . | P8 |
----- \ | . | . | ./ -----
\ | . | . | / .
----- . ----- . ----- .
| P4 |-------| P5 |--------| P6 | .
----- . ----- . ----- .
. . . . . .
. ===== . ===== . =====
. | O1 |----------| O2 |--------| O3 |
. ===== . ===== . =====
. | . | . |
. | . | . |
. | . | . |
. | . | . |
.| .| .|
===== ===== =====
| O4 |----------| O5 |--------| O6 |
===== ===== =====
Figure 1. IP and Optical Layered Network Topology
In Figure 1, P1 to P8 are IP nodes, and O1 to O6 are optical nodes.
Assume we need to deploy a low latency path between P7 and P8.
According to traditional segment routing in IP layer, perhaps we can
choose the path along {P7, P1, P2, P3, P8}. But if an optical path
from O1 to O3 exists, and the End.XU function defined in this
document is used to announce this path into the IP domain with
specific attributes, the headend node or controller in IP domain can
choose the path along {P7, P1, END.XU, P3, P8} which provides lower
latency than the normal paths.
The creation of the optical path from O1 to O3 may be requested
either by the headend IP node P7 or the IP network controller (not
shown in the Figure). The creation should be done by the optical
network controller (not shown in the Figure), so that P7 or IP
network controller needs to inform the path requirements to the
optical network controller. The details of the process are out of
scope of this document, and may refer to [I-D.lee-teas-actn-vpn-poi].
We can also use the topology in Figure 1 to show another use case.
Assume there are two optical paths between P1 and P2. One is {O1,
O2} , and the other is {O1, O4, O5, O2}. We can assign two End.XU
functions for these two underlay paths separately. One is P1::C2 for
the path {O1, O2}, and the other is P1::C45 for the path {O1, O4, O5,
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O2}. The headend P7 or the IP network controller will be informed
about the two SRv6 functions and the associated path attributes, so
that the headend or the controller can program different end-to-end
inter-layer paths using integrated SID lists for services with
different SLA requirement.
Assume the path {O1, O2} is owned by the operator with a higher
reliability, and the path {O1, O4, O5, O2} is not totally owned by
the operator, i.e., they are partly rented. In this use case, for
the traffic with high reliability requirement, the integrated SID
list implemented in P7 would be <P1::C2, ... , P8>. The ellipsis
means some other possible SRv6 functions can be added along the path.
For traffic with normal reliability requirement, the integrated SID
list programmed in P7 can be <P1::C45, ... , P8>. Before the
announcement of the two functions, the node P1 needs to map the
P1::C12 function to the optical path {O1, O2}, and map P1::C45 to the
optical path {O1, O4, O5, O2}.
5. Security Considerations
TBD
6. IANA Considerations
This document defines a new SRv6 function called END.XU.
IANA is requested to allocate four new code points from the "SRv6
Endpoint Behaviors" sub-registry in the "Segment-routing with IPv6
dataplane (SRv6) Parameters" registry:
+-------+--------+---------------------------+-----------+
| Value | Hex | Endpoint function | Reference |
+-------+--------+---------------------------+-----------+
| TBA | TBA | End.XU (no PSP, no USP) | [This.ID] |
| TBA | TBA | End.XU with PSP | [This.ID] |
| TBA | TBA | End.XU with USP | [This.ID] |
| TBA | TBA | End.XU with PSP&USP | [This.ID] |
+-------+--------+---------------------------+-----------+
7. Acknowledgements
The authors would like to thank Xiaodong Chang for his review and
comments.
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8. References
8.1. Normative References
[I-D.ietf-spring-srv6-network-programming]
Filsfils, C., Camarillo, P., Leddy, J.,
daniel.voyer@bell.ca, d., Matsushima, S., and Z. Li, "SRv6
Network Programming", draft-ietf-spring-srv6-network-
programming-01 (work in progress), July 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
DOI 10.17487/RFC2629, June 1999,
<https://www.rfc-editor.org/info/rfc2629>.
8.2. Informative References
[I-D.ietf-isis-l2bundles]
Ginsberg, L., Bashandy, A., Filsfils, C., Nanduri, M., and
E. Aries, "Advertising L2 Bundle Member Link Attributes in
IS-IS", draft-ietf-isis-l2bundles-07 (work in progress),
May 2017.
[I-D.lee-teas-actn-vpn-poi]
Lee, Y., Wu, Q., Busi, I., and J. Tantsura, "Abstract",
draft-lee-teas-actn-vpn-poi-00 (work in progress), October
2018.
Authors' Addresses
Jie Dong
Huawei Technologies
Q14, Huawei Campus, No.156 Beiqing Road
Hai-Dian District, Beijing, 100095
P.R. China
Email: jie.dong@huawei.com
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Zongpeng Du
Huawei Technologies
Q14, Huawei Campus, No.156 Beiqing Road
Hai-Dian District, Beijing, 100095
P.R. China
Email: duzongpeng@huawei.com
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